This invention relates to a speed and distance sensor for providing an electrical output signal from a rotating input shaft. For example, the invention has particular utility in an automotive vehicle where the input shaft is driven by the drivetrain.
In modern automobiles the increasing usage of electronics requires sensors which interface between the electronics and various mechanical components of the automobile. For example it is often desired to sense speed and/or distance for purposes of displaying information and/or control. As such, a sensor may be employed in cooperative association with a mechanical input to provide an electrical output signal correlated with the mechanical input. In the case of an electronic speedometer and/or odometer, a speed and distance sensor can be coupled with the drivetrain of the automobile to provide an electrical signal input to the electronic display containing the speedometer and/or odometer.
Various types of speed and distance sensors are known. Speed and distance are of course mathematically related with speed being the derivative of distance to time. Stated the other way, distance is the integral of speed to time. The nature of the electronic system to which the sensor supplies an input may have a bearing on the nature of acceptable sensor characteristics. For example, one known type of sensor simply produces a train of impulses and the frequency of the pulses is used to provide a speed and distance signal.
The present invention is, in one aspect, directed to a sensor in which it is important to have a characteristic wherein the duty cycle of the output must be closely controlled. A sensor providing this type of a characteristic is required for electronic systems which sample a rectangular waveform in accordance with a particular algorithm for obtaining a speed and/or distance measurement. For this type of usage, a sensor which merely produces a variable frequency pulse without regard to duty cycle characteristics is not an acceptable device.
Moreover, automotive usage imposes severe demands on products. Because of the mass production nature associated with the automobile business, it is important for a sensor to be cost-effective; yet it must be reliable when put to use in a range of extremes involving temperature, humidity, exposure, etc. For example a speed and distance sensor may be located in the engine compartment or in the vicinity of the undercarriage where it is exposed to extreme environmental conditions. An acceptable device must be rugged, reliable, accurate, and cost-effective.
It is also desirable for a speed and distance sensor to be adaptable to different powertrain configurations with no or at most nominal, modification.
The present invention is directed to a sensor which is well-suited for the demands of automotive usage.
One significant attribute of the present invention in the preferred embodiment is that it makes use of a conventional reed switch as the device which provides the electrical output signal. A reed switch is a known component and can be purchased in quantity at reasonable cost. However, such reed switches are not precision components. The present invention enables such a reed switch to provide close control of the duty cycle output and thereby achieve a satisfactory degree of accuracy for automotive usage.
The sensor of the present invention is well-suited to be fabricated as a compact, rugged unit without complicated assembly and fabrication procedures, and without high precision, and hence costly, parts. Because of the unique organization and arrangement of the component parts, it is possible for a magnet which forms a part of the sensor to be fabricated from less expensive magnetic materials than might otherwise be thought appropriate. The invention can also be readily adapted to conform to various automobile powertrain configurations depending upon the specific usage to which it is put. For instance a sensor can be driven by a mechanical speedometer cable, or it can be connected at the transmission.
The foregoing features, advantages, and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.